Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

Optics, X ray and neutron scattering
Birefringence magnétique du vide (BMV)
The LNCMI-T has been engaged since 2001 in a very ambitious experiment to observe the magnetic
birefringence of the quantum vacuum (birefringence magnétique du vide, BMV), an effect predicted in
1935 by Heisenberg and Euler, but never observed so far. The experimental setup has recently reached
a phase where magnetic birefringence of dilute helium gas could be determined with precision, using
pulsed magnetic fields. For the near future, this setup will be further improved, gaining several orders
of magnitude in sensitivity. Major improvements will realize this, such as an upgrade of the
mechanical rotation and tip tilt of polarizers and of the cavity mirrors, the upgrade of the cavity finesse
and its mechanical isolation. Starting from 2011, the BMV experiment will enter in a new phase. The
development and test phase will be completed and an improved apparatus has to be designed to
eventually reach the final goal, the observation of the magnetic birefringence of the quantum vacuum.
A new coil has already been designed for this next phase and tested. It has generated 31.7 T at the
centre and a B²L of about 300 T²m. The goal is to put two of these coils on the experiment, which will
provide sufficient sensitivity to observe the predicted BMV. A new bank of capacitors to supply the
energy for such coils is needed, and is foreseen in the context of the upgrade of the LNCMI-T, in the
form of 6 MJ rapid modules. Once all that in place and properly tested, a long period of data
acquisition will start. A crucial point that has to be studied is if the current room will be able to host
the next generation of set up. A new room can be planned in the context of the extension of the
LNCMI-T building that is also part of the CPER Midi Pyrenees 2007-2013 upgrade project.
To optimally accompany this evolution, Carlo RIZZO, full professor at the University of Toulouse,
and originator of the BMV project, will join the LNCMI starting January 2011. Human and financial
support is also needed to accompany such an experimental effort. We plan to apply to the ERC to
demand such support. The BMV experiment on Cotton-Mouton effect opens a new research line at the
LNCMI. The group has shown that it is now possible to envisage a more general theme: the electromagneto
optics of dilute matter. We are therefore studying the feasibility of measurements of inverse
Cotton-Mouton effects in gases and in vacuum, electro-magnetic Jones birefringence in gases, both
standard and chiral. We plan to adapt the present set up of the BMV experiment to this new line of
research.
X ray and neutron scattering
The use of magnetic fields on X ray or neutron beam lines to study magneto-structural or magnetic
effects is quite common, but so far the field strengths were limited by superconducting magnets to
around 15 T, although a clear scientific case exists to go to much higher fields. A large number of
phenomena has been observed in fields above 15 T, the understanding of which would greatly benefit
from the powerful characterisation possibilities offered by neutron and X ray scattering.
A project is under study to create a static field installation between ILL and ESRF, capable of
generating fields in excess of 30 T to make such fields available for x ray and neutron scattering
experiments. If realized, this project will be completed around 2015. In the mean time, LNCMI-T has
developed a portable pulsed field installation that is actually in use to do such experiments up to 30 T
with pulsed magnetic fields. In collaboration with ILL and ESRF, this installation will be further
improved (see Technical perspectives), new samples environments will be developed in terms of
temperature, pressure and manipulation capabilities, and it will be used for experiments on systems
like quantum magnets, multiferroics, high Tc superconductors etc. This will be done in collaboration
between LNCMI and ILL/ESRF scientists, and qualified external users will also be granted access
through the EuroMagNET Transnational acces procedure.
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